The invention relates to a leadthrough for an electrical high voltage through a wall which separates a process area from an ambient area. The process area has at least in its entrance area an atmosphere which is contaminated by, or includes, liquid droplets (aerosols) and/or carbon or dust particles and which is therefore separated from the environment.
In order to remove such contaminating aerosols or solid particles from the process atmosphere, it is conducted in the process area through cleaning equipment.
Such equipment are for example electrostatic dust collectors or electrostatic wet dust removers. They are generally used for removing contaminants from the air or from gases. The contaminants are removed by being electrostatically charged and then collected on grounded electrodes. To this end, a high electrical voltage must be supplied from a source in the ambient area to the respective high voltage equipment in the process area. Such electrostatic collectors and electrostatically enhanced wet scrubbers remove particles form exhaust gases. In many of the devices developed in the last years, a reduction in size of the devices and increased long-time stability was achieved. Often high voltage leadthroughs extend through the wall or are provided by way of an added structure.
An electrostatic high voltage shield can be used to pre-vent particle deposition on the insulator (see WO 00/30755). In this case, the conductive casing is connected to the same high voltage source as the discharge electrode so that a high voltage electrical field is generated in the area between the casing and the close-by grounded surfaces of the housing. Accordingly, the charged droplets or particles present in the gas are deposited on the grounded surface and not on the high voltage insulators. In order to prevent vapor condensation on the insulators, the insulators are heated since condensation on the insulators could reduce the voltage at the electrical connector. To this end, an electrostatic heater is connected to the insulator in order to maintain it at a temperature of at least 10° C. above the temperature of the surrounding gas. Generally, a few degrees are sufficient to prevent vapor condensation.
The insulators can also be heated by an injection of dry warm cleaning gas into the shield which surrounds the insulators (U.S. Pat. No. 6,156,098 or WO 00/47326. The flow of air around the insulator keeps the surface of the insulator free from moisture and dust deposits so as to keep the insulator clean and generally free from sparking. By the admission of the air by way of a blower or other air pressure generating means to a certain degree air cooling and controlled heating as well as cleaning is provided for in connection with air conditioning in the precipitation device.
U.S. Pat. No. 5,421,863 discloses a self-cleaning venture insulator for an electrostatic precipitator. The insulator consists of a dielectric material into which a spark over can burn only with difficulty. The air flow admitted through a venturi nozzle protects the surface of the insulator from the deposition of impurities from the exhaust gas.
The effectiveness of cleaning the gas depends on a reliable operation of the high voltage supply. Good electrical high voltage insulating materials, which are readily available are important and designs suitable for the ambient area and the process area and particularly the geometries are very important. During operation, the high voltage insulator is exposed to the charged and not charged particles suspended in the gas as well as to the condensed vapors which are possibly present. Over an extended period, the collection of condensed material on the insulator detrimentally affects the insulator. Therefore the insulator must be kept free of impurity deposits so as to avoid sparking. Furthermore, the cleaning intervals must be extended. In addition, the manufacturing costs must be reduced while the insulation properties should be improved.
In this connection, particular attention should be directed to the high voltage leadthrough which is installed in the wall between the ambient and the process area and by way of which the high voltage required for the electrostatic cleaning device can be safely and longtime-reliably provided.